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  • Editor: Bernard Kippelen
  • Vol. 20, Iss. S2 — Mar. 12, 2012
  • pp: A270–A277
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Light-emitting devices with tunable color from ZnO nanorods grown on InGaN/GaN multiple quantum wells

Han-Yu Shih, Shih-Hao Cheng, Jyong-Kuen Lian, Tai-Yuan Lin, and Yang-Fang Chen  »View Author Affiliations


Optics Express, Vol. 20, Issue S2, pp. A270-A277 (2012)
http://dx.doi.org/10.1364/OE.20.00A270


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Abstract

Based on the composite consisting of ZnO nanorods (NRs) grown on InGaN/GaN multiple quantum wells (MQWs), we have demonstrated a novel light-emitting device (LED) that has the capability to emit dual beam radiations. Interestingly, the relative intensity between the dual emissions is able to be manipulated by their polarizations. The underlying mechanism can be well understood in terms of the anisotropic optical properties arising from the geometric structures of constituent nanoscale materials. The results shown here may be extended to many other nanocomposite systems and pave a new pathway to create LEDs with tunable properties.

© 2012 OSA

1. Introduction

2. Experiment

3. Results and discussion

As shown in Figs. 1(a)
Fig. 1 (a) Top view and (b) side view of scanning electron microscope images of InGaN/GaN/ZnO nanocomposite material. (c) X-ray diffraction spectrum and (d) x-ray diffraction spectrum with enlarged scale of 33.6-36.0 degree in (c).
and 1(b), ZnO NRs with around 2.2 μm in length and 100 nm in diameter were well grown on the top surface of InGaN/GaN MQWs. Figures 1(c) and 1(d) show the X-ray diffraction patterns, which reveal well organized lattice via the corresponding peaks of ZnO, GaN, and InGaN [1

1. J. H. Lim, C. K. Kang, K. K. Kim, I. K. Park, D. K. Hwang, and S. J. Park, “UV electroluminescence emission from ZnO light-emitting diodes grown by high-temperature radiofrequency sputtering,” Adv. Mater. (Deerfield Beach Fla.) 18(20), 2720–2724 (2006). [CrossRef]

, 4

4. M. H. Huang, S. Mao, H. Feick, H. Yan, Y. Wu, H. Kind, E. Weber, R. Russo, and P. Yang, “Room-temperature ultraviolet nanowire nanolasers,” Science 292(5523), 1897–1899 (2001). [CrossRef] [PubMed]

, 14

14. Y. T. Moon, D. J. Kim, K. M. Song, I. H. Lee, M. S. Yi, D. Y. Noh, C. J. Choi, T. Y. Seong, and S. J. Park, “Optical and structural studies of phase separation in InGaN film grown by MOCVD,” Phys. Status Solidi, B Basic Res. 216(1), 167–170 (1999). [CrossRef]

]. Since ZnO and GaN have a close lattice constant and the same wurtzite structure, it is expected the growth of ZnO NRs will follow the orientation of GaN substrate [15

15. J. von Pezold and P. D. Bristowe, “Atomic structure and electronic properties of the GaN/ZnO (0001) interface,” J. Mater. Sci. 40(12), 3051–3057 (2005). [CrossRef]

]. Indeed, the X-ray diffraction spectra in Figs. 1(c) and 1(d) reveal this prediction. It means that ZnO and GaN have the same crystalline phase and orientation.

Figure 2(a)
Fig. 2 (a) Illustration of experimental details of electroluminescence measurements for the composited light-emitting device. (b) The current through the light-emitting device as a function of bias voltage. (c) Current dependence of electroluminescence spectra of the composited light-emitting device. (d) Intensities of the 380 nm and 440 nm emissions as functions of the injection current.
illustrates the experimental configuration of electroluminescence (EL) measurements of the composite LED, where the arrow symbols denote the flowing direction of electric current under forward bias. Figure 2(b) shows the current through the LED as a function of the bias voltage, in which we can clearly see that the current-voltage characteristic curve of the device reveals a diode-like behavior. Figure 2(c) shows the current-dependent EL spectra of the LED under forward bias. There are two main EL peaks located at 380 nm and 440 nm in the EL spectra under different forward bias. The two peaks could be attributed to the emissions arising from ZnO NRs and InGaN/GaN MQWs, which could be supported by the evidences given below.

Quite interestingly, when we examine the polarization state of the emission, it is found that the relative intensity between these two EL peaks strongly depends on the polarization as shown in Fig. 4(a)
Fig. 4 (a) Electroluminescence (EL) spectra from the composited light-emitting device through a rotatable polarizer with the angle of 0° and 90°. (b) Polarizer-angle-dependent EL intensities with the monochromator fixed at 380 nm and (c) 440 nm, respectinely. Malus’s-law-fitted lines of 380 nm and 440 nm emissions by Eq. (2) are also shown in (b) and (c).
. Here, 0° is defined as the polarization state parallel to the direction lying in the plane of the MQWs, and 90° is defined as the polarization state parallel to the direction along the growth direction of ZnO NRs (c-axis). In order to understand the polarization property of the LED device more precisely, we fixed the monochromator at 380 nm and 440 nm, respectively, and then recorded the intensity of each EL peak with an interval of 15° of the polarizer angle as shown in Figs. 4(b) and 4(c). Clearly, the intensities of the dual emissions are functions of the angle of polarizer. The result shows that we can obtain the maximum intensity of 380 nm when the polarization axis of the polarizer is parallel to the ZnO nanorod orientation (90°), and the minimum intensity at the perpendicular direction (0°). On the other hand, the emission intensity of 440 nm shows a complementary result that the maximum intensity is at 0° and the minimum intensity is at 90°. As shown in Figs. 4(b) and 4(c), both polarizations of the dual emissions can be described by the Malus’s law quite well [21

21. E. Hecht, Optics, 4th ed. (Addison Wesley, 2002), Chap. 8.

],
I(θ)=Ipcos2(θ+ϕ)+12Iu,
(1)
where I(θ) is the intensity, Ip is the polarized term, Iu is the unpolarized term, θ is the angle of the polarizer as we described before, and ϕ is the phase angle depending on the geometry of structure.

In order to provide more evidences to confirm that the origin of these two emissions arises from ZnO NRs and InGaN/GaN MQWs, we have performed PL measurements on these two materials individually as shown in Fig. 5
Fig. 5 Illustrations of the experimental details and measured spectra under different polarization for (a) InGaN/GaN quantum wells and (b) ZnO nanorods.
. Both samples were grown on sapphire substrates under the same condition as we stated above. The edge emission from ZnO NRs shown in Fig. 5(a) has a narrow line located at 380 nm [3

3. Ü. Özgür, Ya. I. Alivov, C. Liu, A. Teke, M. A. Reshchikov, S. Doğan, V. Avrutin, S.-J. Cho, and H. Morkoç, “A comprehensive review of ZnO materials and devices,” J. Appl. Phys. 98(4), 041301 (2005). [CrossRef]

]. The polarization state of the NBE emission is strongly polarized along the growth direction of ZnO NRs (c-axis). On the other hand, the emission spectrum from the edge of pure InGaN/GaN MQWs exhibits a narrow line located at 440 nm with Fabry-Perot interference patterns as shown in Fig. 5(b) [22

22. T. Y. Lin, “Converse piezoelectric effect and photoelastic effect in InGaN/GaN multiple quantum wells,” Appl. Phys. Lett. 82(6), 880–882 (2003). [CrossRef]

]. The emission was found to be strongly linear-polarized lying on the epitaxial plane (0001). In other words, the polarization states of the emissions of ZnO NRs and InGaN/GaN MQWs are perpendicular to each other. The degrees of polarization for ZnO NRs and InGaN/GaN MQWs are about 56.3% and 62.6%, respectively, via the calculation by the following formula [21

21. E. Hecht, Optics, 4th ed. (Addison Wesley, 2002), Chap. 8.

],
ρ=ImaxIminImax+Imin,
(2)
where ρ is the degree of polarization, Imax is the maximum intensity, and Imin is the minimum intensity. It has been reported that the emitted light from a highly orientational structure is usually linearly polarized due to their anisotropic geometry [5

5. N. E. Hsu, W. K. Hung, and Y. F. Chen, “Origin of defect emission identified by polarized luminescence from aligned ZnO nanorods,” J. Appl. Phys. 96(8), 4671–4673 (2004). [CrossRef]

, 6

6. M. F. Schubert, S. Chhajed, J. K. Kim, E. F. Schubert, and J. Cho, “Origin of defect emission identified by polarized luminescence from aligned ZnO nanorods,” Appl. Phys. Lett. 91, 051117 (2007). [CrossRef]

, 23

23. K. J. Wu, K. C. Chu, C. Y. Chao, Y. F. Chen, C. W. Lai, C. C. Kang, C. Y. Chen, and P. T. Chou, “CdS nanorods imbedded in liquid crystal cells for smart optoelectronic devices,” Nano Lett. 7(7), 1908–1913 (2007). [CrossRef]

25

25. N. F. Gardner, J. C. Kim, J. J. Wierer, Y. C. Shen, and M. R. Krames, “Polarization anisotropy in the electroluminescence of m-plane InGaN–GaN multiple-quantum-well light-emitting diodes,” Appl. Phys. Lett. 86(11), 111101 (2005). [CrossRef]

], therefore, the fact that both samples have their polarization states could be reasonably explained. Because the strongly linear-polarized emissions from these two materials are perpendicular to each other, it could be expected that the emission from the composite consisting of ZnO NRs and InGaN/GaN MQWs should retain the property of each constituent material. Thus, through the manipulation of the properties of the constituent elements, the underlying mechanism of the intriguing property of the dual emissions can be well understood.

4. Summary

In summary, we have demonstrated a novel LED based on the composite consisting of ZnO NRs and InGaN/GaN MQWs. The newly designed LED has the capability to emit dual beam radiations. Quite interestingly, the relative intensity between the dual emissions can be manipulated by a polarizer. The underlying mechanism can be well interpreted in terms of the anisotropic optical properties arising from the geometric structures of the constituent nanoscale materials. Our result presented here can be extended to many other nanostructured composites, and it therefore may open a new pathway for the creation of optoelectronic devices with tunable properties.

Acknowledgments

This work was supported by the National Science Council and Ministry of Education of the Republic of China.

References and links

1.

J. H. Lim, C. K. Kang, K. K. Kim, I. K. Park, D. K. Hwang, and S. J. Park, “UV electroluminescence emission from ZnO light-emitting diodes grown by high-temperature radiofrequency sputtering,” Adv. Mater. (Deerfield Beach Fla.) 18(20), 2720–2724 (2006). [CrossRef]

2.

H. K. Fu, C. L. Cheng, C. H. Wang, T. Y. Lin, and Y. F. Chen, “Selective angle electroluminescence of light-emitting diodes based on nanostructured ZnO/GaN heterojunctions,” Adv. Funct. Mater. 19(21), 3471–3475 (2009). [CrossRef]

3.

Ü. Özgür, Ya. I. Alivov, C. Liu, A. Teke, M. A. Reshchikov, S. Doğan, V. Avrutin, S.-J. Cho, and H. Morkoç, “A comprehensive review of ZnO materials and devices,” J. Appl. Phys. 98(4), 041301 (2005). [CrossRef]

4.

M. H. Huang, S. Mao, H. Feick, H. Yan, Y. Wu, H. Kind, E. Weber, R. Russo, and P. Yang, “Room-temperature ultraviolet nanowire nanolasers,” Science 292(5523), 1897–1899 (2001). [CrossRef] [PubMed]

5.

N. E. Hsu, W. K. Hung, and Y. F. Chen, “Origin of defect emission identified by polarized luminescence from aligned ZnO nanorods,” J. Appl. Phys. 96(8), 4671–4673 (2004). [CrossRef]

6.

M. F. Schubert, S. Chhajed, J. K. Kim, E. F. Schubert, and J. Cho, “Origin of defect emission identified by polarized luminescence from aligned ZnO nanorods,” Appl. Phys. Lett. 91, 051117 (2007). [CrossRef]

7.

H. S. Chen, C. W. Chen, C. H. Wang, F. C. Chu, C. Y. Chao, C. C. Kang, P. T. Chou, and Y. F. Chen, “Color-tunable light-emitting device based on the mixture of CdSe nanorods and dots embedded in liquid-crystal cells,” J. Phys. Chem. C 114(17), 7995–7998 (2010). [CrossRef]

8.

N. Kikuchi, “Analysis of signal degree of polarization degradation used as control signal for optical polarization mode dispersion compensation,” J. Lightwave Technol. 19(4), 480–486 (2001). [CrossRef]

9.

J. R. Law, “Color selection polarizing beam splitter,” U. S. Patent 3497283 (1970).

10.

S. J. Savory, “Digital filters for coherent optical receivers,” Opt. Express 16(2), 804–817 (2008). [CrossRef] [PubMed]

11.

C. Bayram, F. H. Teherani, D. J. Rogers, and M. Razeghi, “A hybrid green light-emitting diode comprised of n-ZnO/(InGaN/GaN) multi-quantum-wells/p-GaN,” Appl. Phys. Lett. 93(8), 081111 (2008). [CrossRef]

12.

M. Guo, P. Diao, and S. Cai, “Hydrothermal growth of well-aligned ZnO nanorod arrays: Dependence of morphology and alignment ordering upon preparing conditions,” J. Solid State Chem. 178(6), 1864–1873 (2005). [CrossRef]

13.

C. F. Huang, C. F. Lu, T. Y. Tang, J. J. Huang, and C. C. Yang, “Phosphor-free white-light light-emitting diode of weakly carrier-density-dependent spectrum with prestrained growth of InGaN/GaN quantum wells,” Appl. Phys. Lett. 90(15), 151122 (2007). [CrossRef]

14.

Y. T. Moon, D. J. Kim, K. M. Song, I. H. Lee, M. S. Yi, D. Y. Noh, C. J. Choi, T. Y. Seong, and S. J. Park, “Optical and structural studies of phase separation in InGaN film grown by MOCVD,” Phys. Status Solidi, B Basic Res. 216(1), 167–170 (1999). [CrossRef]

15.

J. von Pezold and P. D. Bristowe, “Atomic structure and electronic properties of the GaN/ZnO (0001) interface,” J. Mater. Sci. 40(12), 3051–3057 (2005). [CrossRef]

16.

K. W. Jang, D. C. Oh, T. Minegishi, H. Suzuki, T. Hanada, H. Makino, M. W. Cho, T. Yao, and S. K. Hong, “ZnO/GaN heteroepitaxy,” Mater. Res. Soc. Symp. Proc. 829, B10.3.1–B10.3.12 (2005).

17.

E. Fred Schubert, Light-Emitting Diodes, 2nd ed. (Cambridge University Press, 2006), Chap. 4.

18.

E. H. Park, D. N. H. Kang, I. T. Ferguson, S. K. Jeon, J. S. Park, and T. K. Yoo, “The effect of silicon doping in the selected barrier on the electroluminescence of InGaN/GaN multiquantum well light emitting diode,” Appl. Phys. Lett. 90(3), 031102 (2007). [CrossRef]

19.

Z. Z. Bandic, P. M. Bridger, E. C. Piquette, and T. C. McGill, “Minority carrier diffusion length and lifetime in GaN,” Appl. Phys. Lett. 72(24), 3166–3168 (1998). [CrossRef]

20.

J. Y. Wang, C. Y. Lee, Y. T. Chen, C. T. Chen, Y. L. Chen, C. F. Lin, and Y. F. Chen, “Double side electroluminescence from p-NiO/n-ZnO nanowire heterojunctions,” Appl. Phys. Lett. 95(13), 131117 (2009). [CrossRef]

21.

E. Hecht, Optics, 4th ed. (Addison Wesley, 2002), Chap. 8.

22.

T. Y. Lin, “Converse piezoelectric effect and photoelastic effect in InGaN/GaN multiple quantum wells,” Appl. Phys. Lett. 82(6), 880–882 (2003). [CrossRef]

23.

K. J. Wu, K. C. Chu, C. Y. Chao, Y. F. Chen, C. W. Lai, C. C. Kang, C. Y. Chen, and P. T. Chou, “CdS nanorods imbedded in liquid crystal cells for smart optoelectronic devices,” Nano Lett. 7(7), 1908–1913 (2007). [CrossRef]

24.

H. K. Fu, C. W. Chen, C. H. Wang, T. T. Chen, and Y. F. Chen, “Creating optical anisotropy of CdSe/ZnS quantum dots by coupling to surface plasmon polariton resonance of a metal grating,” Opt. Express 16(9), 6361–6367 (2008). [CrossRef] [PubMed]

25.

N. F. Gardner, J. C. Kim, J. J. Wierer, Y. C. Shen, and M. R. Krames, “Polarization anisotropy in the electroluminescence of m-plane InGaN–GaN multiple-quantum-well light-emitting diodes,” Appl. Phys. Lett. 86(11), 111101 (2005). [CrossRef]

OCIS Codes
(230.5440) Optical devices : Polarization-selective devices
(230.5590) Optical devices : Quantum-well, -wire and -dot devices

ToC Category:
Light-Emitting Diodes

History
Original Manuscript: November 28, 2011
Revised Manuscript: February 3, 2012
Manuscript Accepted: February 8, 2012
Published: February 15, 2012

Citation
Han-Yu Shih, Shih-Hao Cheng, Jyong-Kuen Lian, Tai-Yuan Lin, and Yang-Fang Chen, "Light-emitting devices with tunable color from ZnO nanorods grown on InGaN/GaN multiple quantum wells," Opt. Express 20, A270-A277 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-S2-A270


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References

  1. J. H. Lim, C. K. Kang, K. K. Kim, I. K. Park, D. K. Hwang, and S. J. Park, “UV electroluminescence emission from ZnO light-emitting diodes grown by high-temperature radiofrequency sputtering,” Adv. Mater. (Deerfield Beach Fla.)18(20), 2720–2724 (2006). [CrossRef]
  2. H. K. Fu, C. L. Cheng, C. H. Wang, T. Y. Lin, and Y. F. Chen, “Selective angle electroluminescence of light-emitting diodes based on nanostructured ZnO/GaN heterojunctions,” Adv. Funct. Mater.19(21), 3471–3475 (2009). [CrossRef]
  3. Ü. Özgür, Ya. I. Alivov, C. Liu, A. Teke, M. A. Reshchikov, S. Doğan, V. Avrutin, S.-J. Cho, and H. Morkoç, “A comprehensive review of ZnO materials and devices,” J. Appl. Phys.98(4), 041301 (2005). [CrossRef]
  4. M. H. Huang, S. Mao, H. Feick, H. Yan, Y. Wu, H. Kind, E. Weber, R. Russo, and P. Yang, “Room-temperature ultraviolet nanowire nanolasers,” Science292(5523), 1897–1899 (2001). [CrossRef] [PubMed]
  5. N. E. Hsu, W. K. Hung, and Y. F. Chen, “Origin of defect emission identified by polarized luminescence from aligned ZnO nanorods,” J. Appl. Phys.96(8), 4671–4673 (2004). [CrossRef]
  6. M. F. Schubert, S. Chhajed, J. K. Kim, E. F. Schubert, and J. Cho, “Origin of defect emission identified by polarized luminescence from aligned ZnO nanorods,” Appl. Phys. Lett.91, 051117 (2007). [CrossRef]
  7. H. S. Chen, C. W. Chen, C. H. Wang, F. C. Chu, C. Y. Chao, C. C. Kang, P. T. Chou, and Y. F. Chen, “Color-tunable light-emitting device based on the mixture of CdSe nanorods and dots embedded in liquid-crystal cells,” J. Phys. Chem. C114(17), 7995–7998 (2010). [CrossRef]
  8. N. Kikuchi, “Analysis of signal degree of polarization degradation used as control signal for optical polarization mode dispersion compensation,” J. Lightwave Technol.19(4), 480–486 (2001). [CrossRef]
  9. J. R. Law, “Color selection polarizing beam splitter,” U. S. Patent 3497283 (1970).
  10. S. J. Savory, “Digital filters for coherent optical receivers,” Opt. Express16(2), 804–817 (2008). [CrossRef] [PubMed]
  11. C. Bayram, F. H. Teherani, D. J. Rogers, and M. Razeghi, “A hybrid green light-emitting diode comprised of n-ZnO/(InGaN/GaN) multi-quantum-wells/p-GaN,” Appl. Phys. Lett.93(8), 081111 (2008). [CrossRef]
  12. M. Guo, P. Diao, and S. Cai, “Hydrothermal growth of well-aligned ZnO nanorod arrays: Dependence of morphology and alignment ordering upon preparing conditions,” J. Solid State Chem.178(6), 1864–1873 (2005). [CrossRef]
  13. C. F. Huang, C. F. Lu, T. Y. Tang, J. J. Huang, and C. C. Yang, “Phosphor-free white-light light-emitting diode of weakly carrier-density-dependent spectrum with prestrained growth of InGaN/GaN quantum wells,” Appl. Phys. Lett.90(15), 151122 (2007). [CrossRef]
  14. Y. T. Moon, D. J. Kim, K. M. Song, I. H. Lee, M. S. Yi, D. Y. Noh, C. J. Choi, T. Y. Seong, and S. J. Park, “Optical and structural studies of phase separation in InGaN film grown by MOCVD,” Phys. Status Solidi, B Basic Res.216(1), 167–170 (1999). [CrossRef]
  15. J. von Pezold and P. D. Bristowe, “Atomic structure and electronic properties of the GaN/ZnO (0001) interface,” J. Mater. Sci.40(12), 3051–3057 (2005). [CrossRef]
  16. K. W. Jang, D. C. Oh, T. Minegishi, H. Suzuki, T. Hanada, H. Makino, M. W. Cho, T. Yao, and S. K. Hong, “ZnO/GaN heteroepitaxy,” Mater. Res. Soc. Symp. Proc. 829, B10.3.1–B10.3.12 (2005).
  17. E. Fred Schubert, Light-Emitting Diodes, 2nd ed. (Cambridge University Press, 2006), Chap. 4.
  18. E. H. Park, D. N. H. Kang, I. T. Ferguson, S. K. Jeon, J. S. Park, and T. K. Yoo, “The effect of silicon doping in the selected barrier on the electroluminescence of InGaN/GaN multiquantum well light emitting diode,” Appl. Phys. Lett.90(3), 031102 (2007). [CrossRef]
  19. Z. Z. Bandic, P. M. Bridger, E. C. Piquette, and T. C. McGill, “Minority carrier diffusion length and lifetime in GaN,” Appl. Phys. Lett.72(24), 3166–3168 (1998). [CrossRef]
  20. J. Y. Wang, C. Y. Lee, Y. T. Chen, C. T. Chen, Y. L. Chen, C. F. Lin, and Y. F. Chen, “Double side electroluminescence from p-NiO/n-ZnO nanowire heterojunctions,” Appl. Phys. Lett.95(13), 131117 (2009). [CrossRef]
  21. E. Hecht, Optics, 4th ed. (Addison Wesley, 2002), Chap. 8.
  22. T. Y. Lin, “Converse piezoelectric effect and photoelastic effect in InGaN/GaN multiple quantum wells,” Appl. Phys. Lett.82(6), 880–882 (2003). [CrossRef]
  23. K. J. Wu, K. C. Chu, C. Y. Chao, Y. F. Chen, C. W. Lai, C. C. Kang, C. Y. Chen, and P. T. Chou, “CdS nanorods imbedded in liquid crystal cells for smart optoelectronic devices,” Nano Lett.7(7), 1908–1913 (2007). [CrossRef]
  24. H. K. Fu, C. W. Chen, C. H. Wang, T. T. Chen, and Y. F. Chen, “Creating optical anisotropy of CdSe/ZnS quantum dots by coupling to surface plasmon polariton resonance of a metal grating,” Opt. Express16(9), 6361–6367 (2008). [CrossRef] [PubMed]
  25. N. F. Gardner, J. C. Kim, J. J. Wierer, Y. C. Shen, and M. R. Krames, “Polarization anisotropy in the electroluminescence of m-plane InGaN–GaN multiple-quantum-well light-emitting diodes,” Appl. Phys. Lett.86(11), 111101 (2005). [CrossRef]

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